"We do not recognize that regime (Israel), because it is based on occupation and racism," he said during a news conference. "It constantly attacks its neighbors," he said, citing Israeli military action in Syria and Lebanon.
Ahmadinejad also criticized the United States, saying, "We oppose the way the U.S. government tries to manage the world. We think this method is wrong. It leads to war, discrimination and bloodshed."
The Iranian leader, however, downplayed talk of a conflict with the West over Iran's nuclear ambitions, which the United States says is for weapons development but Iran says is for civilian energy use only.
"We think talk of war is a propaganda tool," he said, according to Reuters. "People who talk have to bring a legal reason for war."
Ahmadinejad then visited Columbia University's World Leaders Forum, which prompted protests at the school.
In opening remarks, Columbia President Lee Bollinger criticized Iran's human-rights record and foreign policy, along with Ahmadinejad's statements denying the Holocaust and calling for the elimination of Israel.
"Mr. President, you exhibit all the signs of a petty and cruel dictator," Bollinger said to applause, reported the Associated Press.
He said Ahmadinejad's denial of the Holocaust might fool the illiterate and ignorant. But, "When you come to a place like this it makes you simply ridiculous," Bollinger said. "The truth is that the Holocaust is the most documented event in human history."
Ahmadinejad stood, also to applause, and after a religious invocation, said Bollinger's statement was "an insult to information and the knowledge of the audience here."
"There were insults and claims that were incorrect, regretfully," the Iranian leader said and accused Bollinger of being influenced by the U.S. press and politicians, according to the Associated Press.
Thousands of people stood across the street from U.N. headquarters in New York, protesting the Iranian president's visit. Some sang songs and proclaimed support for Israel. Signs ranged from anti-Ahmadinejad sentiments to those that read, "We refuse to choose between Islamic fundamentalism and American imperialism."
President Bush said Ahmadinejad's appearance at Columbia "speaks volumes about really the greatness of America."
Controversy over Ahmadinejad's visit to the U.N. General Assembly flared when he said he planned to visit Ground Zero, where the Twin Towers collapsed, but New York police denied him access.
U.S. Secretary of State Condoleezza Rice told CNBC that such a visit "would have been a travesty."